1. Field of the Invention
The present invention relates generally to chemical-mechanical polishing systems for use in modifying a substrate by Hertzian indentation, fluid-based wear and/or any similar-type non-microgrinding mechanism; the polishing systems of the present invention are particularly well suited for use in the manufacture of semiconductor devices, memory disks or the like. More particularly, the compositions and methods of the present invention are directed to polishing systems comprising an aqueous based polishing fluid and a fixed abrasive polishing pad.
1. Polishing. xe2x80x9cPolishingxe2x80x9d is intended to mean chemical-mechanical polishing (as opposed to micro-grinding) and is intended to include planarization and any corresponding variations thereof. The polishing substrates contemplated by the present invention include semiconductor device substrates, such as, silicon, silica, gallium arsenide, silicon nitride, tungsten, tantalum, aluminum, copper, and any other semiconductor device substrate, whether conducting, semi-conducting or insulating.
2. Conditioning. In the art of chemical-mechanical polishing, conventional polishing pads generally must be conditioned or otherwise roughened to initially create, then periodically renew, the pad""s polishing surface. Throughout this specification, xe2x80x9cconditioningxe2x80x9d is intended to mean mechanical and/or chemical surface treatment of a pad""s polishing surface to generate nanoasperities.
3. Nanoasperities. Throughout this specification, xe2x80x9cnanoasperitiesxe2x80x9d are intended to mean:
i. protrusions from the pad surface; and/or
ii. particles which release from the pad surface, having an imputed radius (of curvature) of about 0.5 to about 0.1 microns and sufficient resiliency to permanently deform (measured by the permanent change in curvature during polishing) by less than 25%, more preferably less than 10%.
4. Macro-Defects. Throughout this specification, xe2x80x9cmacro-defectsxe2x80x9d are intended to mean burrs or similar-type protrusions on the pad""s polishing surface of greater than 0.5 microns in any dimension.
5. Particles. For purposes of the present invention, xe2x80x9cparticlexe2x80x9d is intended to mean a discrete mass of material as it exists at the polishing interface. Hence, a xe2x80x9cparticlexe2x80x9d can mean an independent, discrete primary particle, an agglomeration of primary particles which form a discrete mass, and/or primary particles which are aggregated together to form a discrete mass. Particles may sometimes be described herein as xe2x80x9chigh modulus phase materialxe2x80x9d or xe2x80x9chigh modulus domainsxe2x80x9d or xe2x80x9cdiscontinuous phasexe2x80x9d.
6. Self-dressing. Self-dressing is intended to mean that the polishing layer abrades, dissolves, wears or otherwise diminishes during the polishing operation, and as it diminishes, new nanoasperities are formed at the polishing interface, whether the pad is periodically conditioned during its useful life or not.
7. Pre-polymer. xe2x80x9cPre-polymerxe2x80x9d is intended to mean any polymer precursor, including an oligomer, monomer, reactive polymer (including cross-linkable or curable polymers) and/or the like.
2. Discussion of the Prior Art
Generally speaking, conventional fixed abrasive polishing systems are used for grinding or micro-grinding of substrates. This type of polishing has been found generally to be inappropriate for improving the planarity of substrates in the manufacture of semiconductor devices or memory disks. Hence conventional polishing systems in the manufacture of semiconductor devices or memory disks generally comprise free abrasive in a polishing fluid and a polishing pad devoid of fixed abrasives.
Such conventional polishing systems generally attempt to improve particle uniformity throughout the polishing interface by flowing large amounts of polishing slurries into the polishing interface and by using slurries with high loadings of abrasive particles. However with such conventional polishing systems, the substrate and polishing equipment generally require extensive cleaning after the polish. This cleaning step slows down production, is prone to operator error and can create environmental concerns.
A need therefore exists in the art for a polishing system which provides improved polishing uniformity along the polishing interface without the need for flowing large amounts of polishing slurries (having high particle loadings) into the polishing interface.
The prior art is exemplified by U.S. Pat. No. 4,343,910 to Busch, Jr. et al. This reference is directed to foamed polymeric materials having a finely divided abrasive. The abrasive has a particle size and a valley abrasion number, the product of which, must fall within a predetermined range; otherwise acceptable polishing is taught to be non-obtainable. Compositions in accordance with this prior art reference are problematic in the polishing of semi-conductor device substrates. Therefore, a need exists in the art for a fixed abrasive polishing system capable of meeting the rigorous polishing performance requirements of the semiconductor industry.
The present invention relates generally to an improved method of chemical-mechanical polishing of one or more substrates useful in the manufacture of semiconductor devices, memory disks or the like, including precursors thereto. In the practice of the present invention, an aqueous fluid (which may or may not contain abrasive particles) is placed between a substrate and a fixed abrasive pad. The fluid preferably provides a substantially consistent pH during polishing. The substrate to be polished is a precursor to a memory disk or a precursor to a semiconductor device.
The pad has a three dimensional fixed abrasive polishing layer. The polishing layer has a plurality of protrusions with recesses between the protrusions. The polishing layer protrusions comprise a plurality of nanoasperities. The polishing layer also contains a plurality of particles having an average particle size of less than 0.6 microns, whereby the average particle size multiplied by the particle""s valley abrasion number is less than 300.
The polishing surface and the substrate surface are moved relative to and are biased toward one another as at least a portion of the fluid is maintained between the surfaces. The fluid between the surfaces acts to prevent at least 20% of the surfaces, on average, from touching one another during polishing.
The surfaces are biased together by applying a uniform pressure of less than 25 pounds per square inch. The polishing surface is compressed by less than 25 microns during polishing, more preferably less than 10 microns and most preferably less than 5 microns. The resulting chemically and mechanically polishing of the substrate surface increases surface planarity.
At least a portion of the particles are released (into the polishing interface) from the fixed abrasive pad during polishing, thereby creating nanoasperities at the polishing interface. The surface area of the fixed abrasive pad at the polishing interface varies by less than 10% during the polishing operation.
The polishing layer has a matrix material as a continuous phase or low modulus phase, and the particles as a discontinuous phase or high modulus phase, and the matrix material has the following properties:
i. a density greater than 0.5 g/cm3;
ii. a critical surface tension greater than or equal to 34 milliNewtons per meter;
iii. a tensile modulus of 0.02 to 5 GigaPascals;
iv. a ratio of tensile modulus at 30 degrees C. to tensile modulus at 60 degrees C. of 1.0 to 2.5;
v. a hardness of 25 to 80 Shore D;
vi. a yield stress of 300-6000 psi;
vii. a tensile strength of 1000 to 15,000 psi; and
viii. an elongation to break less than or equal to 500%.
The matrix material comprises at least one moiety from the group consisting of: 1. a urethane and/or urea; 2. a carbonate; 3. an amide; 4. an ester; 5. an ether; 6. an acrylate; 7. a methacrylate; 8. an acrylic acid; 9. a methacrylic acid; 10. a sulphone; 1. an acrylamide; 12. a halide; 13. an imide; 14. a carboxyl; 15. a carbonyl; 16. an amino; 17. an aldehydric and 18. a hydroxyl.
It has been found that the specified multiplication product (particle size multiplied by the valley abrasion number) is a reliable index of polishing effectiveness. If this product is too high (above 300), good polishing results generally are not achieved; preferably, the multiplication product is below 300, more preferably below 200 and yet more preferably below 100. Particles of less than a micron will generally have valley abrasion numbers of less than 300, more typically less than 200 and yet more typically less than 00. Hence, submicron particles will almost always have a product (particle size multiplied by valley abrasion number) less than 100, more typically less than 200 and most typically less than 300.
Particles of greater than a micron must have a very low valley abrasion number in order to meet the above parameter (i.e., the particle size multiplied by valley abrasion number must be less than 300, etc). In other words, particles having a size greater than a micron must generally be very soft or non-abrasive, to meet this parameter. Such a low valley abrasion number results in particles which are friable under typical polishing conditions, thereby causing such large particles to fracture into pieces which are less than a micron during polishing. Since (for purposes of the present invention), xe2x80x9cparticlexe2x80x9d is intended to mean a discrete mass of material as it exists at the polishing interface, particles in accordance with the present invention will generally be or become submicron in size at the polishing interface.
This invention thus enables those skilled in the art to select an abrasive compound having a suitable particle size and a suitable valley abrasion number such that satisfactory polishing will result when the compound has been incorporated into the specified polymer matrix and the composition is used to polish a surface of a semiconductor device (or integrated circuit) or a precursor thereto.
Polishing in accordance with the present invention is directed to the removal of surface protrusions by severing the chemical bonds between the protrusion and the surface. This mechanism occurs at a molecular level and is much different from micro-grinding. Micro-grinding occurs on a much larger scale, such as by surface fracturing, cutting or abrading, thereby creating unwanted macro-defects. By using the product of particle size and valley abrasion number as a critical parameter of the present invention, the polishing system of the present invention is able to reliably provide chemical mechanical polishing substantially devoid of unwanted grinding or micro-grinding.
Polishing pads in accordance with the present invention comprise a polishing layer created, at least in part, by solidifying a flowable material (including the sintering of flowable solids) into a hydrophilic, polishing layer matrix. Bonded within or onto the polishing layer matrix is a plurality of particulate matter.
The polishing fluid is preferably water based and may also comprise polishing particles (in addition to any particles exposed by or released from the pad). The polishing fluid preferably comprises a pH modifier and optionally a pH buffer, surfactant, chelating agent, and/or oxidizer.
To provide consistency of polishing performance, the polishing pad topography should have a configuration whereby as the pad wears during its useful life, the amount of surface area capable of contacting the substrate changes by less than 30%, more preferably less than 10% and most preferably less than 5%.